With the raise of the conception of Carrier Ethernet (CE), Provider Backbone Transport (PBT) technology, which is a connection oriented Ethernet technology meeting requirements of the telecommunication network, emerges in October, 2005. Thereafter, there are both domestic and foreign providers to network adopting the PBT technology, which has afforded a good beginning for the development of the PBT technology in the Metropolitan Area Network (MAN).
The foundation of PBT technology is the Provider Backbone Bridge (PBB) technology defined in the IEEE802.1ah standard, and is called as Provider Backbone Bridge Traffic Engineering (PBB-TE) by the IEEE. The core of the PBB-TE technology, which is based on the PBB technology, is to improve the PBB technology. The PBB-TE technology uses the Media Access Control (MAC) address of the outer layer in combination with the Virtual Local Area Network (VLAN) identifier of the outer layer, for example, a Backbone Destination MAC address (B-DA)+a Backbone VLAN Identifier (B-VID) to perform service forwarding with a preconfigured forwarding path. Network management and control make the services in the CE have connectivity in practice so as to implement the functions, such as protection switching, Quality of Service (QoS), and traffic engineering and so on, of the telecommunication network. PBB-TE technology is compatible with the architecture of conventional Ethernet bridges, and data frames can be forwarded based on B-DA+B-VID without updating intermediate nodes in the network or modifying the data frames, thus having a high forwarding efficiency.
The PBB-TE technology adopts a Connectivity Fault Management (CFM) mechanism in the IEEE802.1ag standard to continuously monitor the tunnel state in the network. When a working tunnel fails, a service will be automatically transferred to a pre-established protection tunnel, thus increasing necessary flexibility.
Attributes of the tunnel are represented by such a triad of <ESP-DA, ESP-SA, ESP-VID>, in which the parameter ESP-DA refers to the destination MAC address of Ethernet switched path, the parameter ESP-SA refers to the source MAC address of the Ethernet switched path, and the parameter ESP-VID refers to the value of B-VLAN. A point-to-point Traffic Engineering Service Instance (TESI) is composed of a pair of bidirectional point-to-point Ethernet switched paths. Specific description related to the triad and the TESI may see the IEEE802.1Qay standard.
FIG. 1 is a schematic diagram of the full path protection of the PBB-TE tunnel in the related art. The left-to-right direction in FIG. 1 is taken as example, and the ESP of the end-to-end working tunnel Y-B-C-D-X is <B-MAC2, B-MAC1, B-VLAN1>, wherein B-MAC2 is the MAC address of node X, which is the destination MAC address; B-MAC1 is the MAC address of node Y, which is the source MAC address; B-VLAN1 is the value of the B-VID of the end-to-end working tunnel Y-B-C-D-X.
The full path protection is implemented in FIG. 1, wherein Y and X are the ends of the tunnel instance of the end-to-end working tunnel Y-B-C-D-X of the TESI; Y-F-G-H-X is the protection tunnel of the Y-B-C-D-X. When it is detected that Y-B-C-D-X fails, it can be switched to the Y-F-G-H-X, and B-VLANs born on the tunnels are respectively designated for the working tunnel and the protection tunnel, for example, B-VLAN1 is designated to the working tunnel and B-VLAN2 is designated to the protection tunnel, when pre-configuring, for the purpose of distinguishing that a packet is forwarded on the working tunnel or the protection tunnel when forwarding the packet.
The continuity of a tunnel is checked by sending the Continuity Check Message (CCM) defined in the IEEE 802.1ag standard on the tunnel. Ends of the tunnel send CCMs to each other respectively along the working tunnel and the protection tunnel, and the CCM message headers for the working tunnel and the protection tunnel respectively encapsulates B-VLAN1 and B-VLAN2 (see the IEEE 802.1Qay standard).
Although the end-to-end protection technology of the PBB-IE can effectively protect tunnels, the end-to-end protection scheme not only has a relatively long protection switching time, but also involves relatively more nodes. Therefore, when a certain segment of a path is very fragile or a certain segment is very important, protection may be only made for a segment link of the end-to-end tunnel. The protection object of the segment protection domain is one or more protected TESIs born on the working segment in the segment protection domain. FIG. 2 is a schematic diagram of segment link protection of the PBB-TE in the related art. As shown in FIG. 2, B-C-D is the segment bearer link of the end-to-end working tunnels TESI-1 and TESI-2 and is the segment working link, and B-F-G-H-D is the segment protection link. To differentiate from the full path protection of the end-to-end tunnel, the segment link is called as the segment hereafter, i.e., B-C-D is a working segment, and B-F-G-H-D is the protection segment of the B-C-D. When the working segment has a failure, all the protected TESIs on the physical link are switched to the protection segment.
FIG. 3 is a schematic diagram of two segment protection domains with a shared link. As shown in FIG. 3, there are two segment protection domains, segment protection domain1 and segment protection domain 2. The working segment in segment protection domain 1 is the link of B-C, whose protection segment is B-F-G-C; the working segment in protection domain 2 is the link of C-D, whose protection segment is C-G-H-D. C-G is the shared link in the two segment protection domains, wherein C is the shared node in the working segments and the protection segments in the two segment protection domains (PIB for short), and G is the shared node only in the protection segments in the two segment protection domains (AIB for short). It is assumed that a certain TESI is carried on the working segments in the segment protection domain 1 and the segment protection domain 2 and is protected by the two protection domains, and the bidirectional ESPs of the TESI are ESP-1 and ESP-2. A filtering data base (FDB) is stored in the nodes and the FDB contains a plurality of FDB entries, whose normal form is <destination end (DA), ESP-VID>→out port (Out). In a normal case, ESP-1 of the TESI at the Y→X direction is along B-C-D in the protection domain. It is assumed that ESP-VID of ESP-1 is 1, then the FDB entry on the node of the protection domain is configured as the “<X, 1>→Out” entry in the filtering data base above the node in the figure. Similarly, it is assumed that ESP-VID of ESP-2 at the X→Y direction is 2, then the FDB entry on the node in the protection domain is configured as the “<Y, 2>→Out” entry in the filtering data base above the node in the figure.
In a normal case, segment protection domain 1 only needs to pre-configure working entry and standby entry for TESIs protected by the protection domain on the segment ends B and C, and switches between the two entries when a failure occurs. FIG .4 is a schematic diagram of the protection switching when the working link in one of the two segment protection domains with a shared link shown in FIG. 3 fails. As shown in FIG. 3 and FIG. 4, on ESP-1at the Y→C direction, the working entry of node B is “<X, 1>→P2” and the standby entry is “<X, 1>→P3”; on ESP2 at the X→Y direction, the working entry of node C is “<Y, 2>→P1” and the standby entry is “<Y, 2>→P3”. Nodes B and C forward packets according to working entries by default, and when the B-C link fails, nodes B and C switch to their own standby entries for filtering packets.
FIG. 5 is a schematic diagram of the protection switching when the shared node in the two segment protection domains with a shared link shown in FIG. 3 fails. As shown in FIG. 5, when the shared node PIB in the two segment protection domains with a shared link fails, the two segment protection domains switch the ESP-1 and ESP-2 from B-C-D to B-F-G-H-D, and at the moment, the configuration about the FDB entries of the bidirectional ESPs on the' node C (PIB) is unchanged, i.e., the configuration about using which FDB entry to filter packets is unchanged.
If both of the two segment protection domains adopt the non-revertive mode, then the traffic is still carried on the A-B-F-G-H-D-E link after the failure of node C (PIB) recovering. At the moment, the configuration about the FDB entries of the bidirectional ESPs on node C (PIB) is unchanged. FIG. 6 is a schematic diagram of the protection switching when the protection segment in protection domain 1 shown in FIG. 3 fails in the non-revertive mode. As shown in FIG. 6, at the moment, if the link F-G fails, the failure belongs to the failure of the un-shared link in the segment protection domain 1, then node B will switch the FDB entry of ESP-1 to the working entry “<X, 1>→P2”, and node G (AIB) will switch the FDB entry of ESP-1 to “<Y, 2>→P3”. In the node C (PIB), the FDB entry of ESP-1 is still maintained in the working entry “<X, 1>→P2”, and the FDB entry of ESP-2is still maintained in the working entry “<Y, 2>→P1”, and therefore, ESP-1 is along with A-B-C-D-E and ESP-2 is along with A-B-C-G-H-D-E. It can be seen from the figure that ESP-1 and ESP-2 are now not co-routed at this moment, i.e., the bidirectional data streams of one data communication instance are not transmitted on the same path. Likewise, in the segment protection domains with a shared link, the case that bidirectional ESPs are not co-routed will also occur in the case that there is one segment protection domain working in the non-revertive mode. However, IEEE802.1Qay requires that the bidirectional ESPs of a point-to-point TESI should be co-routed, so for the existing segment protection method for Ethernet tunnels, when at least one of the two segment protection domains with a shared link works in the non-revertive mode, the bidirectional ESPs are not co-routed after the protection switching during the period from the working segments passing the two segment protection domains failing simultaneously or the shared node of the working segments failing to the failure recovering, which does not meet the requirement of IEEE802.1Qay.